I have a bike that did not come with gears. It is a rear hub driven ebike with a single speed. Eventually when the warranty runs out, I want to put gears in it and turn it to a mid drive. Now I know that the reasonable thing to do is to just get a bike with gears and put a mid drive in it but I really like the frame, accessories, and mounts it has. Also I am passionate about tinkering and sometimes passion and reason do not really mix.
I have looked at and studied the area I am going to be working on the bike. It has a vertical dropout and the distance between the two inner dropouts is 135mm.
Reading Sheldon Brown's site, it says I can fit a 7, 8, or 9 speed cassette. I had a spare 9 speed Wheelset from a gravel Bike and I let it sit between the dropouts and I verified it fits with disc brakes.
However, the next and hardest piece of the puzzle is finding a derailleur hanger. I know that hangers are specific to each bike, but I'm kind of hoping that there could be one that could work. After browsing through hundreds of hangers out there, I can't seem to find one that may fit the drive side drop out. One thing I noticed though is that dropouts with hangers usually have a notch where the hanger would sit to keep it from moving. My drop out doesn't have that notch.. The only thing that would keep the derailleur from moving would be a small hole for a 4mm hex bolt which is primarily used to hold one side of the rear fender and the axle skewer itself.
If I were to get a derailleur hanger for this frame that may work, I would need to drill a hole in the drive side dropout. This would compromise the integrity of the dropout/ frame which I don't like but is the only way I can see myself bolting a derailleur hanger.
My other option to add gears would be to just get an internal gear hub such as a Shimano Alfine. No drilling or crazy mods involved so the frame would keep its integrity. But I really prefer the derailleur setup over the IGH.. it reminds me of when I was a kid with my first mountain bike..
So my questions are:
Is there something I can bolt on to the rear drop out so I can attach a derailleur hanger? I don't care if it looks weird as long as I can get a derailleur hanger on there
If there is no such part, would drilling a hole to accomodate a derailleur hanger be a viable? Would frame integrity really be compromised that much?